1. Field of the Invention
The present invention relates to surgical instruments for laser cardiac ablation procedures. More particularly, the invention relates to a wand including a fiber optic transmission channel for atrial cardiac ablation.
2. Description of the Prior Art
A. Atrial Fibrillation
It is known that at least some forms of cardiac arrhythmia are caused by electrical impulses traveling through the cardiac muscle tissue by abnormal routes. In a normal, non-arrhythmic heart, electrical nerve impulses travel in an orderly and well-defined fashion through the sinoatrial node and then through the atrioventricular node in order to create an orderly flow of nerve impulses that lead to contraction in the heart.
In cardiac arrhythmia, cardiac impulses travel disorderly and undesirable paths through the cardiac tissue leading to disorderly and inefficient contraction of heart muscle. These fibrillations prevent the heart from pumping blood efficiently and can lead to death.
B. Maze Procedure—Generally
One technique for treating atrial fibrillation is to surgically create lines in the heart muscle tissue (myocardium) whereby electrical conduction of nerve impulses is blocked or rerouted. This technique for creating lines of electrical blockage is referred to as the Maze procedure.
Initial approaches to performing the Maze procedure involved invasive surgery in which a series of linear incisions are made in the cardiac tissue and then sutured together. The lines of scar tissue that form in the incisions do not conduct nerve impulses and are intended to prevent disorderly contraction of the atrial tissue.
In a typical Maze procedure, up to six non-conductive lines are required. Each of the non-conductive lines is typically several centimeters in length. Once these lines scar and heal, they disrupt electrical pathways that may support atrial fibrillation. Examples of the Maze procedure and other surgical techniques for treating atrial fibrillation are described in Chiappini, et al., “Cox/Maze III Operation Versus Radiofrequency Ablation for the Surgical Treatment of Atrial Fibrillation: A Comparison Study”, Ann. Thorac. Surg., No. 77, pp. 87-92 (2004) and Cox, “Atrial fibrillation II: Rationale for surgical treatment”, J. Thoracic and Cardiovascular Surg., Vol. 126, No. 6, pp. 1693-1699 (2003).
C. Less Invasive Maze Procedure Technologies
Less invasive ablation techniques have also been utilized to perform the Maze procedure. In such techniques, the surgeon typically drags an electrode in a linear fashion along the endocardial (internal) or epicardial (external) surface to produce a series of focal lesions. The scaring created by the focal lesions is hopefully contiguous and non-conductive of electrical impulses. For endocardial use, standard ablation catheters or catheters with extended distal electrodes are employed. Epicardially, specially designed handheld probes with a distal electrode for the application of ablating energy are often used.
For the greatest likelihood of success in a Maze procedure, it is particularly important that the lesions created be transmural. A transmural lesion extends through the full wall thickness of the cardiac muscle at the location of the lesion. One factor that obstructs obtaining transmural lesions from an epicardial approach of the heart is the cooling effect of blood in and around the heart. This is a particular difficulty when radio frequency (RF) energy is employed. The application of RF energy relies exclusively on thermal diffusion to create transmural lesions. The cooling effect of blood within the atrium tends to limit the depth to which thermal lesions can be formed.
It is desirable to create a full thickness transmural lesion but undesirable to perforate the atrial wall. Perforation of the atrial wall leads to a weakening of the heart structure as well as significant bleeding during surgery that must be controlled.
Additionally, producing transmural lesions with RF energy tends to heat the surface tissue at the point of probe contact this. This tends to create burns and adhesion between the probe and the heart tissue. Such adhesions can insulate the probe from the heart tissue blocking the efficient application of energy. These procedures are also a problem for the surgeon and staff who often must stop to clean the tip of the probe.
A discussion of techniques and technologies for treating atrial fibrillation is set forth in Viola, et al., “The Technology in Use for the Surgical Ablation of Atrial Fibrillation”, Seminars in Thoracic and Cardiovascular Surgery, Vol. 14, No. 3, pp. 198-205 (2002). Viola et al. describe numerous ablation technologies for treating atrial fibrillation with the Maze procedure. These include cryosurgery, microwave energy, radiofrequency energy, and laser ablation.
D. Laser Ablation and the Maze Procedure                i. Treatment of Atrial Fibrillation with Laser Energy        
The use of lasers in treating atrial fibrillation is desirable. Laser ablation is fast and the resulting lesion is narrow. Viola, et al., “The Technology in Use for the Surgical Ablation of Atrial Fibrillation”, Seminars in Thoracic and Cardiovascular Surgery, Vol. 14, No. 3, pp. 201, 204 (2002). However, in the prior art, laser ablation for treating atrial fibrillation has been troublesome.
Viola et al. discuss problems associated with the use of laser energy to treat atrial fibrillation. These concerns are directed to safety and reliability and note that lasers are prone to overheating because of the absence of a self-limiting mechanism. The authors note that over-heating with lasers can lead to crater formation and eventually to perforation, especially when using pin-tip devices. Viola, et al., sutara, at p. 203. The authors note that the high power of laser ablation (described as 30 to 80 Watts) results in the laser technique not being widely clinically applied. Id., at p. 201. The mechanical effects resulting from direct heating of the myocardial tissue with laser energy results in cellular explosions caused by shock waves. Viola, et al., supra, at p. 201.
The possibility for perforation of the myocardium with laser energy raises a particular concern for treating atrial fibrillation. The myocardial wall of the atria is quite thin (e.g., about 2 mm in thickness in some locations). A coring of the myocardium by a laser could result in a full wall thickness perforation and resulting leakage of blood.
Viola et al. note the development of a long probe laser that allows diffusion of the laser thermal energy over the long probe tip in a unidirectional fashion. Id., at p. 201. While not mentioning the source of this long probe tip, it is believed by the present inventors to be referring to the atrial fibrillation laser of CardioFocus, Inc., Norton, Mass. (USA) as described in U.S. Patent Application Publication No. 2004/6333A1 in the name of Arnold, et al. (published Jan. 8, 2004) and U.S. Pat. No. 6,579,285 issued to Sinosky. Unfortunately, this technology defocuses energy and increases the risk (particularly on a beating heart) of creating a lesion that is less than transmural.                ii. Inapplicability of Ventricular Laser Treatment        
Lasers have been effectively used for treating ventricular tachycardia. An example of such is described in U.S. Pat. No. 5,104,393 to Isner et al. dated Apr. 14, 1992.
Unfortunately, while such laser treatments are appropriate for treating the left ventricle. They are not applicable to treating the atria.
The myocardial wall of the left ventricle is substantially thicker than the atria. Therefore, perforation risks are less. Also, in a ventricular treatment, the laser is targeted against a tissue area for substantial periods of time (e.g., about two minutes). To accomplish this, the lasers have a fixation member at the laser tip. (see, e.g., element 42 in the '393 patent). The lasers may also be provided with a temperature sensing tip as described in U.S. Pat. No. 5,830,209 to Savage et al. dated Nov. 3, 1998. Temperature probes provide a temperature profile at the tissue treatment site. U.S. Pat. No. 5,827,267 to Savage et al. dated Oct. 27, 1998 teaches a multi-fiber laser with recirculating coolant contained by a quartz lens and a 50 to 100 watt power source with irradiation up to ten minutes.
The aforementioned lasers are catheter delivered to project laser energy to the interior (endocardial) surface of the heart in the ventricle. In treating tachycardia as described, the laser is intended to create a lesion of necrosed tissue at a discrete target site. To accomplish this, a high power laser is provided with an anchor or fixation device to hold the laser tip at the target site for a prolonged period of laser irradiation.
Ventricular treatment lasers are not applicable to treating atrial fibrillation. In treating atrial fibrillation, a long, narrow, transmural lesion is desired to be formed in a pathway consistent with the Maze procedure. The high power laser of the ventricular treatment lasers presents risk of damage and perforation of the thin-walled atrium as noted by Viola, et al. Further, the single-point treatment of ventricular lasers (created with the assistance of myocardial fixation) is inappropriate to the objectives of the Maze procedure and the tips of such lasers are not optimized for atraumatic movement over the epicardial surface of the atria.
In the foregoing, applicants have referred to the use of lasers in atrial fibrillation as “ablation” techniques. While the use of the term “ablation” is a common usage when describing atrial fibrillation treatments, such usage is an unfortunate misnomer. In treating atrial fibrillation, there is no intent or desire to ablate tissue to the extent that term implies removal of tissue. In fact, in a strict sense, ablation is to be avoided. As noted in Viola et al, it is undesirable to create perforations through laser ablation. Instead, the desire is to create a full myocardial wall thickness (i.e., “transmural”) lesion of scar tissue or necrosed myocardial tissue which is narrow and remains in situ in the surrounding myocardium to act as a barrier to undesirable transmission of electrical or neural impulses through the myocardium.
In the strict sense of tissue removal, ablation lasers have been used in the ventricle in transmyocardial revascularization (“TMR”) procedures. In TMR procedures, the object is to form a bore from the left ventricle partially through the myocardium with the hope the bore will facilitate the flow of oxygenated blood into ischemic myocardial tissue. Of course, such technology is not applicable to atrial fibrillation treatments were bore formation (or perforations) are to be avoided.
In all types of laser treatments or RF electrode treatments, it is important that the apparatus not damage the tissue through mechanical damage. In ventricular lasers, the traumatic tip does not risk damage to the endocardial tissue since it is immobilized in place with an anchor or fixation as described in the afore-mentioned U.S. Pat. No. 5,104,393. In the afore-mentioned U.S. Patent Application Publication No. 2004/6333A1, such risks are minimized by laying the diffusing probe over the tissue area.
In the present invention, it is contemplated to draw the tip of a laser wand over the surface of the heart in the region of the atria. In doing so, care must be taken to minimize risk of injury to the atria. For example, the atria are very thin walled. Also, while not as abundant in the atria as in the ventricle region, superficial blood vessels reside on the epicardial surface. A moving object should minimize snags or tears.
From the above, while laser treatment of atrial fibrillation is desirable, existing technology has been inadequate. It is an object of the present invention to provide an apparatus and method for treating atrial fibrillation with the benefits of a laser treatment. The surgical art would benefit from a laser probe for creating transmural, non-perforating lesions without the problems of sticking or snagging on the atrial wall tissue. Further, it is desirable that the probe itself not heat up and that energy be efficiently applied to the heart tissue.
E. Conductivity Verification
A further difficulty with creating linear nonconductive lesions is the inability to verify that a truly nonconductive lesion has been produced. If a transmural lesion is not properly formed in accordance with the Maze procedure, the treatment for atrial fibrillation may not be successful. This could require a second surgical procedure. It would be helpful if the surgeon could promptly discern whether a particular linear lesion is truly non-conducting at the time of the original procedure to permit correction at that time. This would enable prompt re-treatment if necessary.
F. Additional Cardiac Ablation Technology
A large variety of devices for cardiac ablation exist in the art. Devices for cardiac ablation combining electrodes and laser include: U.S. Pat. No. 4,785,815 issued to Donald Cohen, U.S. Pat. No. 5,172,699 issued to Robert Svenson et al, U.S. Pat. No. 5,306,274 issued to Gary Long. U.S. Pat. No. 5,769,843 issued to George Abela et al, U.S. Pat. No. 5,824,005 issued to Massoud Motamedi et al, U.S. Pat. No. 6,024,739 issued to Dean Ponzi et al and U.S. Pat. No. 6,200,310 B1 issued to Shlomo Ben-Haim et al.
Devices for cardiac ablation including electrodes but no laser include: U.S. Pat. No. 5,354,296 issued to David Turkel, U.S. Pat. No. 6,063,081 issued to Peter Mulier et al., U.S. Pat. No. 6,161,543 issued to James Cox et al., and U.S. Pat. No. 6,231,518 B1 issued to James Grabek et al.
Device employing laser for cardiac ablation include: U.S. Pat. No. 4,693,244 to Daikuzono, U.S. Pat. Nos. 4,985,028 and 5,104,393 to Jeffrey Isner et al., U.S. Pat. No. 5,282,798 issued to Bruse et al., U.S. Pat. No. 4,955,267 issued to Jacobs, et al., U.S. Pat. No. 5,389,096 issued to Michael Aita et al., U.S. Pat. No. 5,897,551 issued to Everett, et al., U.S. Pat. No. 5,951,541 issued to Simpson, et al., U.S. Pat. No. 6,066,131 issued to Richard Mueller et al., U.S. Pat. No. 6,110,167 issued to Cozean, et al., U.S. Pat. No. 6,135,996 issued to Kolesa et al., U.S. Pat. No. 4,693,244 issued to Daikuzuno, U.S. Pat. No. 5,046,810 issued to Steiner et al and U.S. Pat. No. 5,534,000 issued to Bruce.
Devices for intracardiac use as catheters include: U.S. Pat. No. 5,782,828 issued to Peter Chen, U.S. Pat. No. 5,800,428 issued to Dale Nelson et al and U.S. Pat. No. 6,063,080 issued to Dale Nelson et al.
Devices for epicardial procedures include: U.S. Pat. Nos. 5,380,316 and 5,925,033 issued to Michael Aita et al., U.S. Pat. No. 5,728,091 also issued to Sam Payne et al, U.S. Pat. No. 6,231,568 B1 issued to Marvin P. Loeb et al, U.S. Pat. No. 6,237,605 B1 issued to Matthias Vaska et al.